1. Field Of The Invention
This invention relates to microwave devices in the millimeter wave region, more particularly to scanned, waveguide-type antennas.
2. Description Of The Prior Art
Dielectric waveguide antennas in the millimeter range have generally consisted of two types. They are surface-wave and leaky-wave antennas.
Surface-wave antenna radiation is emitted in a subtantially end-fire direction and occurs due to the truncation of the waveguide. The shape of the radiation pattern is dependent upon the manner of truncation which, by presenting a gradual transition from waveguide cross-section to free-space, may reduce reflection and improve antenna efficiency.
Leaky-wave antennas, the genre of the instant invention, operate on the principle that a small hole in a waveguide (like a water pipe under pressure) will act as a point source radiator, emitting in the direction normal to the point of penetration. If a leaky-wave antenna is properly designed, it radiates a main beam in a sector of sidewards direction.
The principles of leaky-wave antennas are well known and do not form a part of the instant invention. A good treatment of the subject may be found in Collin and Zucker's ANTENNA THEORY, 1969, McGraw and is hereby incorporated by reference.
It is also known in the prior art that a leaky-wave antenna may be swept so as to move the main receptive or transmitting beam through an angle. This sweeping has been accomplished by changing the positional relationship between the E-H wave patterns and the physical geometry of the leaky-wave antenna apertures. One way of accomplishing this is to alter the resonant operating frequency by a permissable amount, such that the frequency stays withinthe safety factor around the chosen operating mode of the waveguide. A better way seems to be to change the phase performance of the dielectric material by an external control means. One such method is shown in U.S. Pat. No. 3,959,794 to Chrepta and Jacobs. In this patent a semiconductor waveguide was used. The phase characteristic of the waveguide is changed by means of PIN diodes which are embedded in one face of the waveguide and are selectively biased on to alter the phase performance. Another known dielectric leaky-wave antenna, described in the 1981 IEEE MIT-S International Microwave Symposium Digest pp. 20-22 teaches a dielectric waveguide embedded in a metal ground plane, one face open to the air and silvered with strips perpendicular to the long axis. Unfortunately, this antenna, though fairly simple in construction, cannot be swept.